This invention relates to a method and apparatus for automotive wheel alignment. More particularly, the invention relates to toe alignment of automotive wheels.
Of the several wheel alignment factors (caster, camber, toe-in and toe-out) the toe alignment is by far the most critical. Probably 95% of all excessive front tire wear is caused by toe misalignments, either toe-in or toe-out. Excessive toe-in causes tires to wear on the outside; toe-out causes tires to wear on the inside. All vehicles have toe adjustments.
Camber, the amount by which the wheel is off vertical when the vehicle is level, is not a measurable tire wear factor. Camber of the front wheels changes continually while the vehicle is in motion. Some vehicles do not even have a chamber adjustment.
Caster, the tilting of the front steering axis backward or forward is the least important of all front end settings. Vehicles with Macpherson struts do not have caster adjustments.
In all automotive vehicles as manufactured, the steering wheel is centered with a rack and pinion, or a pitman arm. Centering allows the steering mechanism to give equal turns to the right and left, and allows the front wheels to go out of parallel the proper amount on turns. If an unknowledgeable mechanic has removed the steering wheel to center the steering, a good alignment job is impossible until the wheel is put in the factory position.
In vehicles with a pitman arm, the pitman and idler arms should be straight ahead or parallel to the frame of the car when the steering wheel is centered. In vehicles with rack and pinion steering, there should be exactly the same amount of turn from the steering wheel center position to the right and left lock positions.
Any looseness in the front wheel bearings, idler arm, or tie rod joints will make it impossible to obtain repeat readings on any alignment system. As vehicle mileage accumulates, the front wheel bearings get loose first, then the idler arm and rarely the tie rod ends. The greatest culprit in front end mechanism wear is out-of-balance front tires, which make the car vibrate and pound all joints and bearings much more than road bumps. One under-inflated front tire will make the vehicle pull in that direction. The more the under-inflation, the greater the pull. This is the most common cause of pulling complaints.
The accuracy of the alignment system of this invention allows the user to check for looseness when reading the alignment of the vehicle. As one of the front wheels is turned 1/8 degree and returned, the other should follow and return. If it doesn't, the looseness should be corrected before the car is aligned.
The alignment system of this invention gives accurate readings on the rear wheels of cars with independent rear suspension.
U.S. Pat. No. 2,249,226 issued July 15, 1941 to Peters is the most relevant prior art that I know of. The Peters patent discloses a light beam projector for mounting to the wheel of a vehicle and for directing a light beam to a calibrated target close to the vehicle. This device is variously used for toe, camber, and caster adjustment. The system and its use are quite different from the present invention.